1. Field of the Invention
The present invention relates to a radar apparatus adapted to be installed on a movable object such as, for instance, a vehicle, and more specifically, to a radar apparatus and a radar signal processing method for measuring the distance and the relative speed of an object to be detected (hereinafter referred to as a “target”) by detecting the target.
2. Description of the Related Art
In general, in such a kind of radar apparatus installed on a movable object such as a vehicle, the detection range of a target is from about a few meters to about several hundreds of meters, so the distance and speed of the target is measured by an FMCW (Frequency Modulated Continuous Wave) method.
According to a known radar apparatus and a known radar signal processing method therefor, the distance R and the relative speed V of a target are calculated according to the following expressions (1) and (2) by using, as a transmitted signal, a continuous wave (FMCW) signal including an up modulation period in which the frequency thereof becomes higher with the lapse of time, and a down modulation period in which the frequency becomes lower with the lapse of time (see, for instance, a first patent document: Japanese patent application laid-open No. H11-271429).R=(fU+fD)/(2×Kr)  (1)V=(fU−fD)/(2×Kv)  (2)where fU represents a beat frequency observed in the up modulation period; fD represents a beat frequency observed in the down modulation period; Kr represents a conversion factor for conversion from distance to frequency; and Kv represents a conversion factor for conversion from relative speed to frequency.
Here, note that in the above-mentioned first patent document, in order to improve target detection performance, the distance R and the relative speed V of the target at the following observation are predicted from those which were calculated at a certain observation (e.g., current observation), and the beat frequencies fU, fD at the following observation are predicted based on the above expressions (1) and (2). Among a plurality of beat frequencies fU, fD obtained at the following observation, a pair of those values which are the nearest to the predicted values are selected so that the distance R and the relative speed V of the target are calculated based on the values thus selected.
In the known radar apparatus and the radar signal processing method, according to the principle of the FMCW type or system, the distance R and the relative speed V of the target are not necessarily calculated from the above expressions (1) and (2) because of a magnitude correlation for the distance R and the relative speed V, and hence there arises a problem that particularly in case where the calculated values of the distance R and the relative speed V are approximate with each other, confusion can be made between the distance R and the relative speed V.